This application claims, under 35 USC 119, priority of Japanese Application No. 2002-191521 filed Jun. 28, 2003.
The disclosure of Japanese Patent Application No. 2002-191521 filed on Jun. 28, 2002 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to an oil pressure control device of an automatic transmission installed in a motor vehicle and, more particularly, to an oil pressure control device of an automatic transmission capable of securing the supply of an engaging pressure to a friction engagement element even if a control valve or the like, which normally supplies the engaging pressure to the friction engagement element, cannot operate normally (hereinafter, referred to as xe2x80x9cfailurexe2x80x9d).
2. Description of the Related Art
Automatic transmission oil pressure control devices (hereinafter, also referred to as xe2x80x9coil pressure control devicesxe2x80x9d) conventionally have a plurality of shift valves, control valves, etc., that are interconnected so as to form a hydraulic control circuit and which are able to appropriately change the shift speed in accordance with operation of a shift lever. Some of such oil pressure control devices are designed to adjust and supply a predetermined range pressure via a control valve to a hydraulic servo of a clutch used at the time of starting the vehicle in motion, such as a clutch C-1.
The control valve mentioned above typically has a spool with a land spacing which is narrower than the port spacing between an input port and a drain port, so as to enhance the responsiveness in controlling the pressure received from a linear solenoid valve or the like. However, with a control valve having such a structure, there is the possibility that small bits of foreign substances in the automatic transmission fluid (ATF) (referred to hereinafter as xe2x80x9coilxe2x80x9d) will cause valve sticking. If such a failure (valve sticking) occurs, there is the danger of loss of good performance in starting the vehicle in motion due to difficulty in supply of the engaging pressure to the clutch C-1. In order to avoid this, an oil passage between the control valve and the clutch C-1 hydraulic servo is provided with a changeover valve that changes over to a different path so as to allow supply of the engaging pressure even if a failure occurs. However, in this structure, there is the possibility that the presence of the changeover valve may reduce the responsiveness of the clutch C-1. The aforementioned valve sticking may also occur in a linear solenoid valve as mentioned above. For example, in the event of intermediate sticking, wherein the spool is stopped at an intermediate position, generally referred to as an xe2x80x9con-statexe2x80x9d (or xe2x80x9coff-statexe2x80x9d) failure, etc., output of the control pressure becomes difficult and it becomes difficult to engage the clutch C-1.
Accordingly, it is an object of the present invention to provide an oil pressure control device for an automatic transmission that is designed so as to secure the supply of the engaging pressure to a friction engagement element even if a failure occurs in a control valve or a linear solenoid valve (solenoid valve), and that thereby solves the aforementioned problems.
In accordance with the present invention, where a pressure adjusting unit includes, for example, a valve structure, and where the pressure adjusting unit is subject to intermediate sticking or the like, so that the output of an engaging pressure becomes difficult, it is possible to supply the original pressure from a second port of the pressure adjusting unit via a connecting oil passage and therefore supply oil pressure to the hydraulic servo.
In the present invention, the changeover valve conventionally provided between a control valve and a friction engagement element is omitted, so that responsiveness of the friction engagement element is improved. Furthermore, the changeover valve disposed between the control valve and the solenoid valve that together form the pressure adjusting unit makes it possible to secure good engaging pressure supply to the friction engagement element even if the control valve or the solenoid valve fails. For example, if the solenoid valve fails so that the output of the control pressure becomes difficult while the control valve is in a normal state, the changeover valve is switched to a second position. Therefore, instead of the control pressure, the original pressure from the connecting oil passage is supplied to the control oil chamber of the control valve, so that, for example, a first port and an output port of the control valve are connected, thus supplying the original pressure to the hydraulic servo. Therefore, in a case where the friction engagement element is a vehicle start clutch, it is possible to achieve, for example, the first forward speed and therefore move the vehicle. Furthermore, if the control valve fails (sticks) with the first port and the output port in communication, while the solenoid valve is in a normal state, the original pressure supplied to the first port can be supplied to the hydraulic servo via these two ports. On the other hand, if the control valve fails with the output port and a second port in communication, the original pressure from the connecting oil passage can be supplied to the hydraulic servo via these two ports.
Even in the case where the land spacing (interval) of the spool of the control valve is narrower than the spacing between the first port and the second port and where a spool becomes stuck at an intermediate position such that communication is not established with either one of the ports (generally referred to as xe2x80x9cintermediate stickingxe2x80x9d), the hydraulic servo can be supplied with the engaging pressure via the upstream and downstream connecting oil passage provided with the one-way valve.
In the present invention, the range pressure supplied via the manual valve can be used as the xe2x80x9coriginal pressure.xe2x80x9d
Accordingly, the present invention makes it possible to favorably cope with a failure of a frequently used vehicle start (launch) clutch.